RE: Turtles and Crocodylians are not Reptiles - no? What are they?

[Tim Williams <twilliams_alpha@hotmail.com>]

Robert Takata wrote:

> Sure. And all fossil represent only a fraction of diversity that had
> ever existed too. Few taxa could be more problematic if we have much
> homoplasy.


I think you're missing the point.  When it comes to Sauropsida/Reptilia, it's 
not just that the vast majority of species have gone extinct, but the vast 
majority of major clades as well.  If turtles and crocs are being drawn 
together by long-branch attraction, and neither birds nor squamates can break 
this up, then all other options are exhausted.   


> My fault here. Normally "fossil" DNA reffer to a conserved DNA
> sequence - somewhat molecular fossil - it could help in somecases. But
> what I've meant is what Boehm said: DNA preserved in fossil.


This hasn't happened yet (for fossil vertebrates, anyway), except for certain 
subfossil taxa.  


> Closer to hippos thant to mesonychids anyway.


Actually, no.  Under Thewissen &c's phylogeny, there is a 3-way polytomy 
(trichotomy) composed of Mesonychia, _Andrewsarchus_ and the 
Cetacea+Artiodactyla clade.  The hippopotamids are inside the crown 
Artiodactyla, in the Suina clade.  Because the whales are recovered in a 
Cetacea-Raoellidae clade at the base of the Artiodactyla, cetaceans are *not* 
closer to hippos than to mesonychians.  Not according to this phylogeny, anyway.


Mike Keesey wrote:

> Wouldn't it be better to restrict Artiodactyla to the crown and just
> say that cetaceans are not artiodactyls; but are their extant
> sister group;, and raoellids are very basal stem-cetaceans.


That would seem to be a very good idea.  Artiodactyla could be restricted to 
the crown artiodactyls; Cetacea could similarly be restricted to the crown 
cetaceans, and another name (Cete?) could be used for Cetacea and 
stem-cetaceans (raoellids, 'archaeocetes'); and the name Cetartiodactyla could 
be co-opted for the least inclusive clade that includes artiodactyls and 
cetaceans.  However, raoellids have traditionally been considered artiodactyls 
(as members of the Suina clade), so this may have influenced Thewissen &c's 
decision to keep Raoellidae inside Artiodactyla (and pull Cetacea along with 
it).


To be honest I don't know how Artiodactyla, Cetacea, and Cetartiodactyla are 
each currently defined.  Thewissen &c studiously avoided the term 
'Cetartiodactyla', even though it's an obvious choice for the 
Cetacea+Artiodactyla clade.  This may have something to do with the fact that 
the Cetartiodactyla concept came about from molecular analyses (just a guess).  


> No Whippomorpha.  Kind of sad....


Not to me.  :-)   I never bought the entire Whippomorpha (= 
Hippopotamidae+Cetacea) thing anyway - despite what (some) molecular 
phylogenies said.  BTW, there are some people who favor(ed) a 
Hippopotamidae-Cetacea clade, but hate(d) the name 'Whippomorpha', and so came 
up with a new name: Cetancodonta.


Cheers

Tim

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